Wheel alignment apparatus and method for vehicles having electro-mechanical power steering

Abstract

A method and apparatus are provided for aligning the wheels of a vehicle equipped with an electro-mechanical power steering system having a steering angle sensor, a torque sensor, and a torsion bar linking the steering angle sensor and the torque sensor. Embodiments include moving a steering wheel of the vehicle to a level position such that there is substantially no torque applied to the torsion bar; adjusting the toe of a first one of the front wheels of the vehicle after the steering wheel is moved to the level position; and moving the steering wheel substantially back to the level position, then re-adjusting the toe of the first one of the front wheels, when the steering wheel has moved more than a predetermined angle from the level position while adjusting the toe of the first one of the front wheels.

What is claimed is: 
     
       1. A method for aligning the wheels of a vehicle equipped with an electro-mechanical power steering system having a steering angle sensor, a torque sensor, and a torsion bar linking the steering angle sensor and the torque sensor, the method comprising:
 moving a steering wheel of the vehicle to a level position such that there is substantially no torque applied to the torsion bar; 
 adjusting the toe of a first one of the front wheels of the vehicle after the steering wheel is moved to the level position; 
 aligning the rear wheels of the vehicle prior to adjusting the toe of the first one of the front wheels; 
 calculating the thrust angle of the rear wheels; 
 measuring the toe angles of each of the front wheels; 
 determining whether the steering wheel has moved more than the predetermined angle based on each of the front wheel toe angles relative to the thrust angle; and 
 moving the steering wheel substantially back to the level position, then re-adjusting the toe of the first one of the front wheels, when the steering wheel has moved more than a predetermined angle from the level position while adjusting the toe of the first one of the front wheels. 
 
     
     
       2. The method of  claim 1 , comprising:
 adjusting the toe of a second one of the front wheels when the steering wheel has moved less than the predetermined angle from the level position while adjusting the toe of the first one of the front wheels; and 
 moving the steering wheel substantially back to the level position, then re-adjusting the toe of the second one of the front wheels, when the steering wheel has moved more than the predetermined angle from the level position while adjusting the toe of the second one of the front wheels. 
 
     
     
       3. The method of  claim 1 , comprising adjusting at least one of caster and camber of each of the front wheels after aligning the rear wheels and prior to adjusting the toe of the first one of the front wheels. 
     
     
       4. The method of  claim 1 , comprising determining the vehicle is equipped with an electro-mechanical power steering system prior to moving the steering wheel to the level position. 
     
     
       5. The method of  claim 1 , wherein resetting the steering wheel substantially back to the level position comprises turning one of the front wheels. 
     
     
       6. The method of  claim 1 , wherein the electro-mechanical power steering system has an electronic control unit in communication with the steering angle sensor and the torque sensor, the method comprising activating the electronic control unit prior to adjusting the toe of the first of the front wheels. 
     
     
       7. The method of  claim 1 , wherein the vehicle has an electronic control unit for controlling a suspension component of the vehicle, the method comprising:
 placing the vehicle on an alignment rack having a locking turntable under each of the rear wheels prior to alignment the rear wheels of the vehicle; 
 performing a roll back procedure; 
 unlocking the turntables under the rear wheels after performing the roll back procedure; and 
 starting the engine of the vehicle to reset the electronic control unit after unlocking the turntables. 
 
     
     
       8. An apparatus for aligning the wheels of a vehicle equipped with an electro-mechanical power steering system, the apparatus comprising:
 measuring devices for determining toe angles for each of the front and rear wheels of the vehicle; and 
 a data processor coupled to the measuring devices and having a set of instructions that, when executed, cause the data processor to perform the steps of: 
 calculating a thrust angle of the rear wheels based on the toe angles of the rear wheels received from the measuring devices; 
 prompting a technician to move a steering wheel of the vehicle to a level position without locking the steering wheel; 
 establishing the level position of the steering wheel based on each of the front wheel toe angles, received from the measuring devices, relative to the thrust angle; 
 prompting a technician to adjust the toe of a first one of the front wheels of the vehicle; 
 determining whether the steering wheel has moved more than a predetermined angle from the level position while adjusting the toe of the first one of the front wheels based on a change in the toe angle of a second one of the front wheels; 
 prompting the technician to move the steering wheel substantially back to the level position, then re-adjust the toe of the first one of the front wheels, when the steering wheel has moved more than the predetermined angle from the level position while adjusting the toe of the first one of the front wheels; and 
 determining whether the steering wheel has moved more than the predetermined angle from the level position while re-adjusting the toe of the first one of the front wheels based on a change in the toe angle of the second one of the front wheels. 
 
     
     
       9. The apparatus of  claim 8 , wherein the set of instructions is for causing the data processor to perform the steps of:
 prompting the technician to adjust the toe of the second one of the front wheels when the steering wheel has moved less than the predetermined angle from the level position while re-adjusting the toe of the first one of the front wheels; 
 determining whether the steering wheel has moved more than a predetermined angle from the level position while adjusting the toe of the second one of the front wheels based on a change in the toe angle of the first one of the front wheels; and 
 prompting the technician to move the steering wheel substantially back to the level position, then re-adjust the toe of the second one of the front wheels, when the steering wheel has moved more than the predetermined angle from the level position while adjusting the toe of the second one of the front wheels. 
 
     
     
       10. The apparatus of  claim 9 , comprising a display device for indicating the steering wheel level and toe angles of each of the front wheels, for guiding the technician when aligning the front wheels and leveling the steering wheel. 
     
     
       11. The apparatus of  claim 10 , wherein the display device is for displaying the thrust angle such that the technician can discern if the thrust angle changes during wheel alignment. 
     
     
       12. The apparatus of  claim 11 , wherein the data processor is for causing the display device to graphically display the steering wheel level, toe angles of each of the front wheels, and thrust angle. 
     
     
       13. The apparatus of  claim 8 , wherein the data processor is for prompting the technician to reset the steering wheel substantially back to the level position by turning one of the front wheels. 
     
     
       14. The apparatus of  claim 8 , wherein the electro-mechanical power steering system has an electronic control unit, and the data processor is for prompting the technician to activate the electronic control unit prior to adjusting the toe of the first of the front wheels.